1. Field of the Invention
The present invention relates to a power semiconductor device and a method of fabricating the same.
2. Description of the Related Art
An insulated gate bipolar transistor (IGBT) refers to a transistor in which a gate is manufactured using a metal oxide semiconductor (MOS) and a p-type collector layer is formed on a rear surface to thereby have bipolarity.
Since a power metal oxide semiconductor field effect transistor (MOSFET) according to the related art has been developed, the MOSFET has been used in a field requiring fast switching characteristics.
However, due to structural limitations of the MOSFET, a bipolar transistor, a thyristor, gate turn-off thyristors (GTOs), and the like have been used in technical fields requiring high voltages.
The IGBT having low forward loss and fast switching speed characteristics has been widely applied to a field in which it is impossible to use an existing thyristor, a bipolar transistor, a metal oxide semiconductor field effect transistor (MOSFET), or the like.
Describing an operational principle of the IGBT, in the case in which the IGBT device is turned on, an anode thereof has a voltage higher than that of a cathode applied thereto, and in the case in which a gate electrode has a voltage higher than a threshold voltage of the device applied thereto, polarity of a surface of a p-type body region disposed at a lower end of the gate electrode is reversed, to thereby form an n-type channel.
An electron current injected into a drift region through a channel derives an injection of hole current from a high density p-type collector layer located below the IGBT device similar to a base current of the bipolar transistor.
Due to a high concentration injection of a few carriers as described above, a conductivity modulation, increasing conductivity in the drift region from tens to hundreds of times, may occur.
Unlike the MOSFET, since a resistive component in the drift region may be significantly reduced due to the conductivity modulation, an application of high voltage is possible.
Current flowing toward the cathode is divided into electron current flowing through the channel and hole current flowing through a junction between the p-type body and the n-type drift region.
The IGBT is a p-n-p structure between the anode and the cathode in the substrate structure. Therefore, since a diode is not embodied in the IGBT, unlike in the case of the MOSFET, separate diodes should be connected in an inverse-parallel manner.
The above-mentioned IGBT has largely major characteristics such as maintenance of blocking voltage, a decrease in conduction loss, and an increase in a switching speed.
According to the related art, a magnitude of the voltage required for the IGBT is increased and durability of the device is required to be increased.
However, in accordance with miniaturization of the device, in the case in which the magnitude of the voltage is increased, latch-up is generated due to a structure of the device, such that the device may easily break down.
The latch-up refers to that in the case in which a p-n-p-n parasitic thyristor, structurally present in the IGBT, is operated, the IGBT enters a state in which it is no longer adjusted by a gate, such that a significant current may flow in the IGBT and the device may overheat and break down.
In addition, in accordance with the miniaturization of the device, a short circuit may be generated in the IGBT.
Such a short circuit, largely generated in a case of a load connected to the device, for example, an inductive load such as a motor, refers to a case in which a current is applied to the gate in a state in which a high voltage is applied to the IGBT, such that a high voltage and a large current are simultaneously applied to the IGBT.
Short circuit immunity of the IGBT is evaluated as a time for which the device withstands such pressure without being broken down in the above-mentioned short circuit state.
Therefore, in order to secure the miniaturization and reliability of the IGBT, a scheme of securing robustness for the latch-up and increasing short circuit immunity is required.
However, current density and short circuit immunity of the IGBT have a trade-off relationship with each other.
Therefore, a scheme of simultaneously developing and improving current density and short circuit immunity is required.
The following related art document relates to an insulating gate type semiconductor apparatus.
The insulating gate type semiconductor apparatus described in the above-mentioned Related Art Document has a constant thickness of a gate insulating film formed on a surface of the gate, but only has a difference in terms of a size of a contact, unlike the present invention.
In addition, the Related Art Document does not disclose a configuration in which a preventing film is formed on an immunity improving unit, unlike the present invention.